Optimizing physical parameters in fault-tolerant quantum computing to reduce frequency crowding

Patent metadata

Field	Value
Publication number	US-9978020-B1
Application number	US-201715473011-A
Country	US
Kind code	B1
Filing date	Mar 29, 2017
Priority date	Mar 29, 2017
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

A technique relates to quantum error correction. Code qubits are configured as target qubits, and the code qubits have a first dephasing time and a first anharmonicity. Syndrome qubits are configured as control qubits, and the syndrome qubits have a second dephasing time and a second anharmonicity. The target qubits and the control qubits are configured to form one or more controlled not (CNOT) gates. The first dephasing time is greater than the second dephasing time and the second anharmonicity is greater than the first anharmonicity.

First claim

What is claimed is:

1. A circuit for quantum error correction, the circuit comprising:
code qubits configured as target qubits, the code qubits having a first dephasing time and a first anharmonicity; and
syndrome qubits configured as control qubits, the syndrome qubits having a second dephasing time and a second anharmonicity, wherein the target qubits and the control qubits being configured to form one or more controlled not (CNOT) gates, wherein the first dephasing time is greater than the second dephasing time and the second anharmonicity is greater than the first anharmonicity.

2. The circuit of claim 1 , wherein one syndrome qubit of the syndrome qubits is configured to be coupled to four of the code qubits.

3. The circuit of claim 1 , wherein a bus resonator is configured to include two code qubits of the code qubits and two syndrome qubits of the syndrome qubits.

4. The circuit of claim 3 , wherein the two code qubits are configured to be coupled together.

5. The circuit of claim 4 , wherein the two syndrome qubits are configured to be coupled to the two code qubits.

6. The circuit of claim 1 , wherein the first dephasing time is a length of time for which the code qubits maintain a given superposition of states, and the second dephasing time is a length of time for which the syndrome qubits maintain a given superposition of states.

7. The circuit of claim 1 , wherein the first anharmonicity denotes a deviation of the code qubits from being a harmonic oscillator, and the second anharmonicity denotes a deviation of the syndrome qubits from being a harmonic oscillator.

8. The circuit of claim 1 , wherein the code qubits are transmon qubits.

9. The circuit of claim 1 , wherein each of the syndrome qubits is a loop of Josephson junctions shunted by a capacitor, the loop having more than two Josephson junctions.

10. A method of configuring a circuit for quantum error correction, the method comprising:
configuring code qubits as target qubits, the code qubits having a first dephasing time and a first anharmonicity; and
configuring syndrome qubits as control qubits, the syndrome qubits having a second dephasing time and a second anharmonicity, wherein the target qubits and the control qubits are configured to form one or more controlled not (CNOT) gates, wherein the first dephasing time is greater than the second dephasing time and the second anharmonicity is greater than the first anharmonicity.

11. The method of claim 10 , wherein one syndrome qubit of the syndrome qubits is configured to be coupled to four of the code qubits.

12. The method of claim 10 , wherein a bus resonator is configured to include two code qubits of the code qubits and two syndrome qubits of the syndrome qubits.

13. The method of claim 12 , wherein the two code qubits are configured to be coupled together.

14. The method of claim 13 , wherein the two syndrome qubits are configured to be coupled to the two code qubits.

15. The method of claim 10 , wherein the first dephasing time is a length of time for which the code qubits maintain a given superposition of states, and the second dephasing time is a length of time for which the syndrome qubits maintain a given superposition of states.

16. The method of claim 10 , wherein the first anharmonicity denotes a deviation of the code qubits from being a harmonic oscillator, and the second anharmonicity denotes a deviation of the syndrome qubits from being a harmonic oscillator.

17. The method of claim 10 , wherein the code qubits are transmon qubits.

18. The method of claim 10 , wherein each of the syndrome qubits is a loop of Josephson junctions shunted by a capacitor, the loop having more than two Josephson junctions.

Assignees

• IBM

Inventors

• Gambetta Jay M
• Magesan Easwar

Classifications

• H03M13/6362

  by puncturing · CPC title

• H03K19/00346 Primary

  Modifications for eliminating interference or parasitic voltages or currents · CPC title

• H03M13/1575

  Direct decoding, e.g. by a direct determination of the error locator polynomial from syndromes and subsequent analysis or by matrix operations involving syndromes, e.g. for codes with a small minimum Hamming distance · CPC title

• G06N99/00

  Subject matter not provided for in other groups of this subclass · CPC title

• H03M13/01

  Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes · CPC title